Silent mortar



J. JQDRISCOLL SILENT MORTAR April 14, 1970 3 Sheets-Sheet 1 Filed April 18, 1967 ATTORNEYS April 1970 J. .1. DRISCOLL 3,505,924

SILENT MORTAR Filed April 18. 1967 5 Sheets-Sheet 2 FIG.3

FIG.6

INVENTOR.

JOHN J. DRISCOLL ATTORNEYS April 1970 J. J. DRISCOLL 3,505,924

SILENT MORTAR Filed April 18, 1967 3 SheetsSheet 5 INVENTOR.

JOHN J. DRISCOLL BY ATTQRNEYS Patented Apr. 14, 1970 3,505,924 SILENT MORTAR John J. Driscoll, Paris, France, assignor to Allied Research Associates, Inc., Concord, Mass., a corporation of Delaware Filed Apr. 18, 1967, Ser. No. 631,650 Int. Cl. F41f 1/06' US. Cl. 891 8 Claims ABSTRACT OF THE DISCLOSURE A mortar with a projectile having a cylinder which contains the propellant, and a piston within the cylinder which pushes upon a rod within the mortar tube to accelerate the projectile. The piston contains the expanded propellant charge and silences the operation.

Mortars are widely used infantry weapons and provide supporting heavy fire power for light infantry and other mobile units. The typical mortar has a heavy steel tube to contain the explosive gases and guide the projectile into the proper path. To keep unit weights down a separate base plate is normally provided. Even the 60 millimeter mortar, the smallest in present use by American forces, is normally broken down into a two-man load for travel over difiicult terrain or long distances. The larger mortars must be broken down to be transported.

The fact that prior mortars have used the mortar tube structure to withstand the propellant charge forces has resulted in the above weight problems and made the mortars more difficult to transport. In addition, the charge is free to expand into the atmosphere once the projectile leaves the tube. These expanding charges create a characteristic noise which serves to inform the energy both as to the type of weapon and its location. At night the flash is visible as the projectile leaves the tube, giving a visible indication of the location. Accordingly, both during the day and during the night enemy fire power may be directed rather accurately at the mortar crew.

Most existing mortars, even the small 60 millimeter mortars, have a propellant system involving a basic charge with supplemental charge increments. The mortar range is a function of the angle of the tube and the number of increments used with the basic charge. While this charge system gives extended range capabilities, its adds unnecessary complications for a very portable mortar suited for used by advanced elements. Specific and detailed personnel training is required. Furthermore, either extensive data must be committed to memory, or the firing tables must be available and readable at the time of firing. Thus additional problems are created, particularly for a small group which would prefer to remain undetected in the nighttime.

My invention avoids the above problems and provides a lightweight, silent mortar suited for use by unskilled personnel. The mortar tube is fabricated from lightweight material and an initiating rod is positioned at the center of the base of the tube. The projectile contains a propellant within a cylinder in its lower portion. A piston and firing pin contained within this cylinder serve to initiate propulson upon impact with the initiating rod. A safety plug prevents inadvertent firing and allows the mortar tube to be used as a carrier for the projectiles. The piston serves to contain the expanded propellant charge so that there is no noise, blast or fiash due to expanding gases from the charge. The projectile velocity is subsonic so that the over all operation is silent. The base may be formed at the angle for an average launch range, with a bubble sight provided for more accurate range determination. Certain embodiments modify the ballistic trajectory to deter even radar location of the silent, flashless mortar operation.

The invention is more fully set forth in the following description in conjunction with the drawings, wherein:

FIGURE 1 is an over-all elevation view in cross-section of the mortar with a projectile in position for firing;

FIGURE 2 is an elevation view in cross-section of the projectile at the moment of firing within the mortar tube;

FIGURE 3 is an elevation view in cross-section of the projectile after leaving the initiating rod;

FIGURE 4 is a perspective view of the mortar sight;

FIGURE 5 is a plan view of bubble sight details;

FIGURE 6 is a view in cross-section of the over-all mortar assembly utilized as a carrying container;

FIGURE 7 is an elevation view in cross-section of an embodiment with a firing hammer;

FIGURE 8 is an elevation view in cross-section of a cylinder assembly employing a consumable piston; and

FIGURE 9 is an elevation view in cross section of an embodiment providing reaction propulsion.

The over-all construction of the silent mortar is shown in FIGURE 1. The mortar tube 2 is terminated in a base portion 4. Since the mortar launching tube of this invention does not need to contain explosive pressure, the tube and base may be molded as one unit from plastic material. Fiber glass reinforcement gives adequate strength to withstand the rough treatment of combat handling. If desired, the tube 2 may be of metal, for example a lightweight alloy, and the base either screwed or molded to one end of the tube. The light tubes of my invention are of sufficiently low cost to be considered expendable items. The initiating rod 6 should be an elongated structure of rigid material, such as metal.

The projectile 8 may be provided with any conventional fuse 10. With the projectile 8 a cylinder 12 is provided with an opening orifice 14 toward the rear. A safety plug 18 closes the orifice to prevent accidental firing. Threads 16 in the rear of piston 22 engage plug 18 to prevent accidental firing through shock if the projectile is dropped. The projectile is thus safe for normal handling. The body of the projectile 8 will normally be fabricated of metal to provide the necessary structure for desired high-explosive, fragmentation, shaped charge or other characteristics. Fins 7 may be provided to furnish spin stabilization or activate spin-actuated components. The safety plug may be of metal but may be more cheaply provided as a molded plastic product. While the plug 18 is shown threaded into the piston 22, economies in manufacture can be obtained by providing a plug with a molded deformable ring. The piston may then be threaded or simply have a mating ring or groove. If the plug 18 must be unthreaded for removal, turning of the piston 22 may be prevented by some deviation from a perfectly uniform radius of cylindrical cross-section in cylinder 12 or by a light staking or adhesive spot. If a deformable plug is used, it may be simply pulled or pried out.

One possible sequence for the firing operation, and the elements involved, are shown in FIGURE 2. The projectile 16 with the safety plug 18 removed, has fallen upon the initiating rod 6. The initiating rod 6 drives the firing pin 24 attached to piston 22 against the primer 26. The flash from the primer 26 ignites the propellant charge 20. As the propellant charge 20 expands, the piston 22 is forced toward the rear of the cylinder 12. Since the initiating rod 6 is fixed within the base 4, the projectile is forced upwards and towards the open end of the mortar tube 2.

FIGURE 3 shows the shell in cross-section just after it has left the initiating rod. The piston 22 is now forced against the compressible sealing ring 28 which abuts shoulder 29. Thus the expanded gases 30 formed by the propellant charge 20 are contained within the cylinder 12. A compressible soft plastic such as polyethylene is suitable for the sealing ring 28. The provision of concentric rings 32 on the base of the piston 22 will help assure a positive seal. The effective seal need be of only very short duration, since sealing is no longer of concern once the projectile reaches its target.

During nighttime attack this mortar is suitable for use without any sight whatsoever by utilizing the angle 34 at which the bottom portion 36 of the base 4 is aligned with the longitudinal axis 38 as shown in FIGURE 1. This angle 34 may be fabricated to provide the average range expected in normal operations. At shorter ranges the tube may be held slightly more toward the vertical, and conversely at longer ranges the tube may be somewhat lowered. 'Ihus adequate accuracy for attack situations may be provided with no sight whatsoever. No tables need to be remembered; no adjustments need to be observed.

For more accurate fire, the simple sight shown in FIGURE 4 may be utilized. A level bubble 58 is attached to the mortar tube 2. The attachment contains a rod 40 affixed to the tube with its outward end 42 expanded into a circular area. Bubble container 44 has an extended member 46 with a pointed end 48. A wing nut 54 on stud 52 of member 46 serves to fasten the bubble holder 44 in a fixed position. A scale 56 operates in conjunction with pointer 48 to provide an indication of the range which will be obtained at that elevation. To operate the sight the soldier need merely loosen the wing nut 54, move the pointed member 48 to the desired range, and retighten the wing nut 54. Then the tube 2 is elevated until the bubble 58 is centered in the member 44. No calculations are required, and no tables need to be read or remembered.

For more precise nighttime operation, the end of pointer 48 may be bent slightly and protrude into depressed scale markings 56. Thus the range may be set by use of the sense of feel in total darkness. If desired, the pointer and range markings may be luminous. To permit bubble leveling in darkness, a phosphorescent marking with crossed arms 51, 53 is provided under the index marking 50 of the bubble sight, as shown in FIG- URES 4 and 5. With an opaque fluid 55, the arms 51, 53 will only be visible as the bubble reduces the opaque fluid thickness. If the transverse arm 51 is in the center and the lengths of the longitudinal arm 53 and the bubble 58 are equal, precise adjustment may be made in total darkness.

FIGURE 6 illustrates the use of the mortar tube 2 as a carrying container. A handle 60 is provided at the center of gravity of the loaded tube. This handle may be either permanently aflixed to the tube at the time of manufacture or subsequently attached by screws or any conventional fabrication technique. If the sight of FIGURE 4 is provided, the bubble container 44 can be configured as shown and serve as the carrying handle. The open end of the tube is provided with a cap 62 which may be molded of one piece of plastic. If an internal ring or projection 64 and an external overlap 66- are provided, the cap will snap into position quite securely and provide good weather protection.

With a typical projectile and tube dimensions approximately three projectiles 8 will fit within the tube 2. The safety plugs 18 will keep the initiating rod 6 from firing the projectiles. The inner-projecting portions 64 of the cap can be dimensioned to fit against the lead projectile 8 to serve as a shock absorber and prevent rattling of the assembly. While the capacity of the carrier can be increased approximately one round by providing a removable initiating rod 6, it is anticipated that the military services would normally prefer to have the tube immediately operable and to eliminate the possibility that the rod 6 be lost in darkness or confusion.

Since the tube 2 can be fabricated cheaply from lightweight materials, the additional rounds may be shipped and supplied in mortar tubes. Therefore, there is no problem in matching weapons and projectiles since they automatically come together. With the extremely simple operation discussed above, an isolated infantryman can operate the mortar. Inpresent practice, only a portion of those in the infantry receive training and are competent to fire motrars effectively. With the mortars of this in vention, every forward element, even an individual rifle squad, may have the heavier support provided by mortars. In addition, various specialized projectiles, such as flares, may be utilized.

The above-described silent projectiles may also be fired from conventional infantry firearms to serve as rifle grenades. Some rifle designs are provided with a separate launching arrangement for rifle grenades. With the silent mortar projectiles, an extension of the barrel itself or the terminal portion of the original barrel, if it is free of projections or irregularities, can serve as the initiating rod 6. In that case, operation is as described above in connection with FIGURES 2 and 3, except that the rifle barrel serves as the initiating rod. If desired, the initiating impact of the projectiles may be manually augmented. In addition to the advantages of not requiring either a grenade launcher attachment or cartridges, much longer ranges are possible than with conventional launchers. Furthermore, rifles may remain ready and loaded with standard ball ammunition.

An embodiment suitable for remote operation is shown in FIGURE 7. The mortar is provided with a hammer 15 within a hollow rod 6. A release pin 17 may then be pulled from a remote location, or by a trip wire, to permit the spring 19 to drive the hammer 15 against the piston 22 to cause the piston to strike the primer 26 and initiate firing as described in connection with FIGURE 2. If it is desired to use this embodiment without the hammer operation, the release pin 17 is inserted into a lower hole 13 in the hammer 15. The hammer then protrudes sufficiently so that it acts as the fixed initiating rod 6 of FIGURE 1. With the release pin in its normal position in hole 11, the hammer does not extend beyond the hollow tube 6'. Shoulders 21 in the mortar tube 2 prevent the projectiles from dropping to a point which would cause undesired firing of the projectile before the release pin 17 is pulled. To reposition the hammer 15 after firing, or after positioning for use as an initiating rod, the flexible member 23 attached to the lower end of hammer 15 is pulled. It will be apparent to those skilled in firearms design that many other hammer designs are possible, and the embodiment shown in FIG- URE 7 is one inexpensive way to provide an expendable mortar suitable for remote operation.

With the hammer operation of FIGURE 7 the firing operation does not depend on the momentum of the projectile as it is dropped down the tube. For rifled operations, steep grooves 25 are provided in the tube 2 and the projectile is provided with lands 9 to engage the rifling grooves. While ignition is possible in a rifled tube without the provision of a hammer, a hammer may be preferable for remote firing. For most applications, a simple tube utilizing a fin stabilized projectile is suflicient. With the simple mortar of FIGURE 1, remote operation may be provided by a release pin 17 in the upper portion of the tube. The release pin will keep the round from falling, and its removal will permit the projectile to drop and initiate firing.

While cylindrical cross-sections have been used for the pistons, cylinders, and initiating rods of the abovedescribed embodiments, almost any desired cross-section may be used so long as it is uniform over those portions in mating contact. While machining operations will normally be slightly cheaper with cylindrical cross-sections, almost any uniform cross-section is equally suitable for east or molded components. For any projecile with a preferred angular orientation, keying through some departure from a circular cross-section should be provided. For example, the initiating rod 6 can be square in cross-section and pass through a square orifice 16. Similarly while pro- 'ectiles are customarily cylindrical, they do not need to be so for the present mortar, and the cross-section can be rectangular if desired. In such case the tube would be of matching cross-section. Such non-circular cross-sections for the projectiles provide a mechanism for giving a predetermined angular orientation to the projectile.

As discussed above, the present invention avoids the conventional methods of mortar site detection by sound ranging or visual flash, smoke or glow locating. With the embodiments of FIGURES 8 and 9 detection by radar locating may be avoided. In the embodiment of FIG. 8 a consumable piston 22. is provided. In this embodiment the primer 26' has been placed on top of the piston 22' and the firing pin protrusion 24' is in the top of the cylinder 12. The primer ignites the upper portion 70 of the piston which serves as the propellant and drives the piston down to launch the projectile. The central lower portion 71 of the piston 22' is composed of material which will burn through after the projectile has left the mortar. The material 71 is tapered or otherwise shaped to hold it in place and prevent premature release of gases with a resulting flash or blast. After material 71 burns through, there will then be a rush of the confined gases through the orifice 14, which may be configured as a nozzle 31. The additional propulsive boost provided will cause the projectile to deviate from a pure ballistic trajectory. The range scale will be based on calculations, or test firings, which take this deviation into account.

Radar ranging operates by extrapolating back along the observed ballistic trajectory. Thus the deviation from a ballistic trajectory causes a displacement of the radar calculated mortar location from the actual location. Still further deviation may be provided by the slower burning component 72 of the consumable piston, if more than one material is employer. The material 72 continues to burn and expel gases, so that a rocket-type trajector due to reaction propulsion is provided over part of the flight.

If desired, a non-burning piston can be provided and trajectory deviation and range extension be provided by one or more auxiliary nozzles 31', as shown in FIG. 9. These nozzles may be angled to impart rotation, if desired. Ports 76 and 78 are provided in the cylinder 12 to communicate with an annular chamber 80 containing propellant 82. When the piston 22 reaches the end of the cylinder as the projectile leaves the mortar, the ports 76 and 78 are uncovered and permit ignition of the propellant. Gases from the propellant issue through nozzle 31 to provide rocket operation. Longer range is achieved and a nonballistic trajectory provided.

To avoid early detection of the projectile, the ports 76 and 78 of FIG. 7 may be plugged with consumable material. The projectile then has an initial silent, flashless trajectory, followed by a later rocket-type flight portion.

While the invention has been described in certain preferred embodiments, those skilled in the weapon arts will recognize that various modifications may be made in materials or details of construction. For example, since the tube does not need to contain pressures, it can be a lightweight open frame structure, with a thin protective film, if desired for weather or dirt protection.

Having thus described my invention, I claim:

1. A weapon comprising a projectile with a cavity containing a propellant charge, a piston within said cavity, said piston comprising consumable materials, an elongated structure adapted to fit into an opening to said cavity, whereby expansion of the propellant charge causes the piston to thrust against the elongated structure and thus accelerate the projectile and combustion of said consumable piston permits a predetermined delayed escape of gases from said cavity.

2. A weapon according to claim 1 wherein a passage connects said cavity with a second region of propellant material whereby combustion of said piston uncovers said passage to permit ignition of said second region of propellant material during the flight of said projectile, whereby there is no release of propellant gases from said second region of propellant material from said projectile until a predetermined time at which said second region of propellant material provides rocket-type propulsion to said projectile.

3. A weapon according to claim 2 wherein at least one passage provides a connection with a second region of propellant material, said second region is provided with an exit opening permitting reaction propulsion of the projectile, and time delay means is provided in said connection to said second propellant region to delay initiation of said reaction propulsion.

4. A weapon comprising a projectile with a cavity containing a propellant charge, a second region of propellant material, a piston within said cavity, said piston having a solid cross-section transverse to the longitudinal axis of said cavity which provides an imperforate barrier across the entire transverse cross-section of the cavity, an elongated structure adapted to fit into an opening to said cavity, whereby expansion of the: propellant charge causes the piston to thrust against the elongated structure and thus accelerate the projectile, and a passage connecting said cavity with said second region of propellant material whereby travel of said piston uncovers said passage to permit ignition of said second region of propellant material during the flight of said. projectile, whereby there is no release of propellant gases from said projectile until a predetermined time at which said second region of propellant material provides rocket-type propulsion to said projectile.

5. A weapon according to claim 4 wherein said passage provides a connection with said second region of propellant material, said second region is provided with an exit opening permitting reaction propulsion of the projectile, and time delay means is provided in said connection to said second propellant region to delay initiation of said reaction propulsion.

6. A weapon comprising a projectile with a cavity containing a propellant charge, a piston within said cavity, said piston incorporating a solid, one-piece cross-section transverse to the longitudinal axis of said cavity, said solid cross-section providing an imperforate barrier across the entire transverse cross-section of the cavity, a primer independent of said piston and adapted to ignite said propellant charge, and an elongated structure adapted to fit into an opening to said cavity, whereby expansion of the propellant charge initiated by said primer causes the piston to thrust against the elongated structure and thus accelerate the projectile.

7. A weapon according to claim 6 wherein said piston is provided with a firing pin protrusion, whereby force from said elongated structure against the piston causes said piston to drive said firing protrusion and the primer together to detonate the primer and initiate expansion of said propellant charge.

8. A weapon comprising a projectile with a cavity containing a propellant charge, a piston within said cavity, said piston incorporating a solid, one-piece cross-section transverse to the longitudinal axis of said cavity, said solid, cross-section providing an imperforate barrier across the entire transverse cross-section of the cavity, said cavity being provided with a firing pin protrusion, said propellant charge being provided with a primer on a side adjacent to said firing pin protrusion, and an elongated structure adapted to fit into an opening to said cavity, whereby force from said elongated structure against the piston causes said piston to drive said firing pin protrusion and primer to gether to detonate the primer and initiate expansion of said propellant charge, whereby expansion of the propellant charge initiated by said primer causes the piston to thrust against the elongated structure and thus accelerate the projectile.

(References on following page) References Cited UNITED STATES PATENTS Berdan.

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Jasse 10249.1

8 3,104,523 9/1963 ODonnell. 3,134,330 5/1964 Batou. 3,306,163 2/1967 Griessen.

BENJAMIN A. BORCHELT, Primary Examiner S. C. BENTLEY, Assistant Examiner 

